Wave signal receiver



Oct. 27, 193,6.

N., P. CASE WAVE S IGNAL RECEIVER Filed Feb. 19, 1935 3 Sheets-Sheet 1 ATTORN E Oct. 27, 193'6.

N.P. AsE WAVE SIGAL RECEIVER FileaFeb. 19, 1955 3 Shee'ts--Sheel 2 1NVENTOR. /VELsa/v /2 C555 ATTORNEY.

ocr. 27, 1936. N. P. CASE 2,058,565

WAVE SIGNAL RECEIVER Filed Feb.- 19, 1935 :5 sheets-Sheet, 3

I C/ e f/ 2 ul b 5y /00 /W/cRol/aLTS f/VPUT /VELso/v P. Casi ATTORNEY.

Patented Oct. 27, 1936 WAVE SIGNAL RECEIVER Nelson P. Case, Bayside, N. Y., assignor to Hazeltine Corporation, a corporation of Delaware Application February 19, 1935, Serial No. 7,169

6 claims. (ci. 25o-20) My invention relates to wave signal receivers and, while it is of general application, it is particularly suitable for embodiment in radio broadcast receivers for use in automobiles or other vehicles.

In certain types of installations of radio broadcast receivers, as, for example, in automobiles, there obtains a relatively high'and substantially constant ambient noise level. It is desirable and necessary that a receiver operating under lsuch conditions shall reproduce a signal with sufficient volume to be "heard clearly over the noise level. However, the maximum volume output of most such radio broadcast receivers is rather limited and, if the volume controlof a receiver is adjusted to give a relatively high output when the coefficient of modulation ofl the carrier wave to which the y receiver is tuned is low, substantial overload with consequent distortion, may occur should the coeilcient of modulation be substantially increased or should the receiver be tuned to a carrier wave having a higher coeicient of modulation. It has been proposedheretofore to control the volume output of radio broadcast receivers by controlling the amplification of a. certain stage or stages thereof in inverse relation tothe intensity of the carrier wave being received, usually as determined by the current output of the detector of the receiver. Such an arrangement, alone, may not, under the conditions just described, provide suiiiciently close control of the volume output of the receiver., Moreover, without the provision of certain additional features, such a receiver tends to amplify to an objectionable extent noises occurring during the tuning from one station to another or when the receiver is not tuned to any station. In addition, such automatic volume control, as it is termed, will not compenprovide a wave signal receiver suitable for operation in surroundings having a high ambient noise level which will reproduce a signal with such intensity as to be heard clearly over the noise level, irrespective of the intensity or the coefficient of modulation of the carrier wave which is being received, and which will, at the same time, avoid the above-noted disadvantages of the arrangements of the prio; art.

More specifically, it is an object of my invencoefiicients of modulation of the carrier waves to which the receiver may be tuned.

In accordance with my invention, a wave signal receiver., including an audio-frequency amplifler, is provided with means for controlling the amplification of one or more of the amplifying or converting stages preceding the audio-frequency ampliferin inverse relation to the coeilicient of modulation of the carrier wave being received and for simultaneously controlling the amplication of one or more of such stages in inverse relation to the intensity of the carrier wave. In accordance with a specific embodiment of my invention, a rectiiier circuit is connected to be energized from the output of the audio-frequency amplifier and to develop a biasing voltage varying in accordance with the output of the audio-frequency amplifier. This biasing voltage is applied to the amplification control electrodes of one or more of the preceding amplifying or converting tubes of the receiver. In addition, a biasing voltage derived from the detector circuit is applied to the amplification control electrodes of one or more of the preceding tubes to assist in maintaining ,the volume output within desired limits, land. to minimize noises produced when the receiver is tuned toan unmodulated carrier wave. For a better understanding of my invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring now to the drawings, Fig. 1 is a circuit diagram of a complete radio broadcast receiver embodying my invention in which certain conventional portionsare indicated schematically since, per se, they form no part of my present invention; Fig. 2 is la circuit diagram of a receiver similar to that of Fig. l but including a modified form of my invention; while Figs. 3 and 4 are curves showing certain operating characteristics of a typical broadcast receiver embodying my invention.

Referring, now, more particularly to Fig. 1 of the drawings, there is shown diagrammatically a complete broadcast receiver embodying my in- I stages, such as a radio-frequency amplifier l2,

an oscillator-modulator I3, and one or more intermediate-,frequency amplifiers H. The intermediate-frequency amplitler Il is coupled Vby means of atuned coupling transformer I5 to a connection.

The detector circuit just vdescribed is coupled to the amplifier section of the tube I6 through the adjustable connection I8a. and a blocking coil 29 of a loudspeaker 30.

condenser 2|, which is connected to the amplification control electrode or grid I6d. A leak resistor-24 is connected from the grid I6d to ground to completethe direct-current circuit between grid and cathode. A biasing resistor 22 may be included in the connection from the cathode I6c to ground, preferably by-passed by a condenser 23. The output of the amplifier section of the tube I6 is coupled by means of a resistor 25 to the input section of an audio frequency amplifier 21, the other terminal of the resistor 25 being connected to any suitable source of unidirectional voltage, as indicated by the symbol +B.' A'radiofrequency by-pass condenser 26 is connected between the anode |6e and ground. The output of the audio-frequency amplifier 21 is fed through an audio-frequency transformer 28 to the moving A condenser 3| may be connected across the output ofthe amplifier 21, as indicated, in order to lessen the response to signals of high audio frequency. The iield 32 of the loudspeaker 30 may be energized from any suitable source' of uni-directionalv voltage.

In case it is desired to compensatethe output ofthe receiver for variations in intensity of the carrier wave being received, negative biasing voltages varying in relation to the intensity of the carrier are impressed upon the amplification control electrodes of one or more of the vacuum tubes of the: radio-frequencyA amplifier I2, the oscillator-modulator I3, and the intermediatefrequency amplifier I4. To this end, the connections 33, 34 and 35 to the amplification control electrodes of the tubes of the stages I2, I3 and I4, respectively, are supplied with biasing voltages by connection to suitable points of a voltage divider circuit comprising serially connected resistors 39, 40, 4|, 33a, 34a, and 35a. This voltage divider circuit is effectively connected across the resistor IB from which is derived a unidirectional voltage varying withthe intensity of the carrier wave being received. The relative values .of the several resistors of the voltage divider circuit determine the portions of the volume control that are effected in the several stages.. Filtering resistors 36 and'condensers 31 are preferably included in one or more of the connections 33, 34 and 35.

The apparatus tl'ius far described is essentially a conventional radio broadcast-receiver of the superheterodyne type provided with automatic amplification control, and its operation need not be described in detail. In brief, signal-modulated carrier waves impressed upon the input circuit Il! are amplified by the tuned radio-frequency amplifier I2, the output of which is imized to modulate the carrier Wave, producing a difference frequency or intermediate frequency which is impressed upon, and amplified by, one

or more stages of intermediate-frequency ampli- By the above-described connections, the detector current owing through the resistor I8 develops thereacross a biasing potential the polarity of which is such that the upper terminal of this resistor is negative` with respect to its lower terminal, Which is connected to ground through the resistor 22. 'I'his negative biasing voltage varies in magnitude in accordance with the amplitude of the carrier wave .being received and is impressed upon the amplification cit'rl electrodes of one or more of the tubes of the amplifying or converting stages I2, I3 and I4 whereby their amplification or conversion gain is varied in inverse relation to the amplitude of the carrier wave being received. This feature is disclosed and claimed in U. S. Letters Patent No. 1,879,863, granted September 27, 1932 on an application of Harold A. Wheeler.

As stated above, when such a broadcast receiver is installed in surroundings having a relatively high ambient noise level, there is a tendency for the receiver to be overloaded, with consequent distortion and other deleterious effects, when the coeficient of modulation of the particular carrier wave being received is relatively high. This consequence is avoided in the abovedescribed receiving system by virtue of `an additional biasing voltage derived from the output of the audio-frequency amplifier 21 and applied to one or more of the amplifying or converting stages preceding the detector; that is, the output of the audio-frequency amplifier 21 is applied betweenthe auxiliary anode I6b and the cathode |6e of the tube I6 through the condenser 38 and condenser 23. The rectification of this audio-frequency current by the electrodes |6c, I6b results in charging the condenser 38 with its lower terminal negative. A leakage vpath for the condenser 38 is provided through the reconnections 33, 34 and 35 to the amplification control electrodes of the tubes of the amplifiers and modulator I2, I3 and I4, respectively. Such a circuit arrangement results in varying the ampliiication of the stages I2, I3 and I4 in in-f' verse relation to the coemcient of modulation of mthe carrier wave being received and tends'to maintain more nearly constant the volume output at the loudspeaker 36; that is, to a'tten the output volume characteristic of the receiver.

In Fig. 2 is shown diagrammatically a broadcast receiver similar to that 0f Fig. '1, but including fa. modified form of my invention. In the main, the circuit is the same as that of Fig. 1 and corresponding elements thereof are identified by the same reference characters. In the circuit `of Fig. 2, however, the additional biasing voltage for controlling the amplification of one or more of the amplifying or converting stages preceding the detector is derived from a voltage divider 43 connected across the output of the amplifier 21 and provided with an adjustable contact 43a. As indicated by the dotted lines, the adjustable contacts I8a andl 43a are mechanically interconnected by a uni-control def vice to be operated simultaneously but in opposite senses; that is, in case the adjustable contact I8a is moved upwardly to increase the volume output of the receiver, the adjustable contact -43a is moved downwardly to decrease the portion of the output voltage of `the amplifier 21 impressed between the electrodes I6b and I6c of the tubev I6.

In the arrangement of Fig. 2, also, the biasing voltage derived from the carrier and that derived from the output of the audio-frequency ampliiier are not combined to control the amplication of each of the several stages, but the automatic volume control bias voltage derived from the resistor I8 is applied to the amplication control electrode of only one of the stages,

for example, the intermediate-frequency amplifier I4; while the automatic volume control bias- `bias voltages, but embraces any of the many combinations thereof jointly to control the amplification or conversion of the signal in the several stages of the receiver.

The operation-of this last-described arrangement is essentially the same as that of Fig. 1. However, when the adjustable contact I8a is set for maximum volume, no audio-frequency voltage is fed back through the connection 43a to the diode elements I6b and I6c so that the system operates exactly as a conventional receiver unmodified by my present invention. At the vsame time, by adjusting the connections |80l and 43a, as, for example, when receiving a carrier waveof a relatively higher intensity, any desired portion of the audio-frequency voltage may be utilized for control purposes without producing any instabilityl or other unfavorable ef- Iects when the volume control setting is again increased for receiving a carrier wave of lower intensity.

While it will be apparent that the impedance valuesvof the several circuit elements of' the above-described system may be varied within wide vlimits in accordance with the particular requirements and desired characteristics of the system, the following constants for the control circuit Iof my invention have been found to be satisfactory in a particular installation.

Condenser 37 ...'microarad-- 0.03 Condenser 38 dn 0.003 Condenser 42 ...,-1 do 0.1 Resistor' 39----. L... --megohm 1 Resistor 40 do 0.5 Resistor 41 do 0.5

'rse relative magnitudes ,er resistere is, asa. fm, ne, 1|, and n win be determined by Moreover, while the sources ot operating voltage for the heating element of the cathode lic and for the other operating electrodes have not been shown, it will be apparent that any conventional source of operating voltage, such as appropriate batteries or a rectiiier and filter circuit, may be utilized. 'I'hese features have been omitted for the sake of brevity since they constitute no part of my present invention and are well understood by those skilled in the art.

The desirable characteristics of the above-described radio broadcast receiver will be best appreciated by consideration of Figs. 3 and 4 of the drawings, which depict certain operating characteristics of a typical broadcast receiver both with and without the features of my invention.

The curves of Fig. 3 show the audio-frequency output of a typical receiver, for an input of 100 micro-volts, as a function of the modulation percentage both with and without the embodiment of my invention. In this figure the dashed curves A, B and C represent the characteristics of a receiver without my invention for three different settings of the volume control I8a', while the solid curves A', B and C represent those of a receiver modied in accordance with my invention, with the volume control |80. adjusted for the same loutput at 40% modulation. It is apparent from these curves that the variation of the output level of a receiver modied in accordance with my invention, with variations in the coeiiicient of modui lation, is materially reduced as compared with that of a similar receiver lacking myinvention; that is, the output characteristic is nearly fiat for wide variations of the coeilcient of modulation. I The curves of Fig. 4 are similar to those of Fig. 3 but with an input oi' 10,000 microvolts. the

dashed curves D, E and F representing the characteristics of the receiver with my invention omitted, and the solid curves D', E and F', the corresponding characteristics of the sainereceiver modied in accordance with my invention. It-is to be noted that the output characteristics are substantially the same even at this of signal input.

While I have described what I at present consider the preferred embodiments of my invention,

higher level it will be apparent to those skilled. in the art that various changes and modiilcations may be made therein without departing from my invention and I. therefore, aim in the appended claimsto cover all such changes and modifications as fall within the true scope and spirit of my invention.

What is claimed is: A

1. In a signal-modulated carrier wave system,

the combination of a carrier-frequency ampliiier- I tube having an amplication control electrode,a

detector coupled to said amplifier, aresistor con\ tector, a condenser and a second resistor leectively connected in series across the output circuit of said audio-frequency amplifier, a rectifier connected in circuit with said second resistor Whereby there is developed across said second resistor a unidirectional voltage varying in accordance with the output of said audio-frequency amplifier, and a circuit for applying said last-named unidirectional voltage as a bias to said control electrode.

2. In a signal-modulated carrier wave system, the combination of a carrier-frequency amplifier, a detector, and an audio-frequency amplifier connected in cascade, means for adjusting the output level of said audio-frequency amplifier, means for compensating for variations in the coefiicient of modulation of a carrier wave comprising adjustable means for controlling the amplification of said carrier-frequency amplifier in inverse relation to the vamplitude of the output of said audio-frequency amplifier, and unicontrol means for simultaneously adjusting said output level adjusting means and said amplification control means.

43.*In a signal-modulated carrier Wave system, the combination of a carrier-frequency amplifier tube having an amplification control electrode. a detector coupled to said amplifier tube, an audiofrequency amplifier, an adjustable coupling between said detector and said audio-frequency amplifier, means for compensating for variations in the coefficient of modulation of a carrier wave comprising a voltage divider effectively connected across the output of said audio-frequency amplifier, means for deriving a unidirectional biasing voltage from said voltage divider and impressing it on said control electrode, and unicontrol means for simultaneously adjusting said voltage divider and said adjustable coupling.

4. In a signal-modulated carrier wave system, the combination of a carrier-frequency amplifier tube having an amplification control electrode, a detector coupled to said amplifier, a signal-frequency amplifier, an adjustable'coupling between variations in the coefcient of modulation of a carrier wave comprising a voltage divider effectively connectedacross the output of said signalfrequency amplifier and provided with an adjustable connection, means for deriving a unidirectional voltage from said voltage divide.' and impressing it negatively on said control elfctrode, and unicontrol means lfor adjusting the connection of said adjustable coupling in a sense to increase the coupling and for adjusting the connection of said voltage divider in a sense to decrease said unidirectional voltage, and vice-versa.

5. In a superheterodyne receiver including a plurality of signal-translating stages, a detector, and an audio-frequency amplifier connected in cascade, meansfor adjustingthe output level of said audio-frequency amplifier, means for compensating for variations in the coeiiicient of modulation of a carrier wave comprising adjustable means for controlling the amplification of at least one of said signal-translating stages in inverse relation to the output of -said audio-frequency amplifier, and unicontrol means for simultaneously adjusting said output level adjusting means and said amplification control means.

6. In a signal-modulated carrier wave system, the combination of a carrier-frequency amplifier, a detector, and an audio-frequency amplifier connected in cascade, means for compensating for variations in intensity of received carrier waves comprising means for controlling -the amplification of said carrier-frequency amplifier in inverse relation to the intensity of the carrier wave, means for adjusting the output level of said audiofrequency amplifier, means for compensating for variations in the coeiiicient of modulation of a carrier wave comprising adjustable means for controlling the amplification of said carrierfrequency amplifier in inverse relation to the amplitude of the output of said audio-frequency amplifier, and unicontrol means for simultaneously adjusting said output level adjusting means and said last-mentioned amplification control 

